This Mystery Plant is found from Maine to Georgia

By John NelsonUSC Herbarium

Thursday, June 6, 2013

Photo by Linda Lee/USC Herbarium--
This plant is at once recognizable. In full bloom, it is a marvelous addition to the roadside flora, easily recognizable. Although it has many close relatives, in the same genus, none of the others form bushy growths like this one.

One of the mysteries surrounding this beautiful native species involves a common name by which it sometimes goes: "Horsefly weed." I don't have a clue where this name comes from; if you know, please tell me: it’s probably a great story. [Common names are a lot of fun, of course, but they are also often misleading and somewhat confusing. Recently, someone was asking me about a plant in his yard, a plant that I identified as a species of Monarda, in the mint family, and I told him that its common name was “Bee-balm”. Turns out that this gentleman knew a different plant as “Bee-balm”, and he sent me a picture of it: a species of Centaurea, in the aster family, which I had always heard called “Bachelors buttons”, or “Raggedy sailors”. Oh well, there just aren’t any rules involved with the use of common names.]This week’s Mystery Plant is a member of the bean family, and is fairly common from Maine south to Georgia, and then inland through all of West Virginia and down into Tennessee and Kentucky. It is less common in the Midwest, probably reaching its western limit in Wisconsin. It is fond of dry, open habitats, and is at home in sandy places. It has been important as a source of herbal medicines, and was widely used by Native Americans. It was also used as a substitute for the indigo of commerce, and has achieved something of a reputation as a native dye plant.The plants, when large enough, are highly branched, and bushy. The stems and foliage are quite smooth, sometimes bluish and waxy looking. The leaves are very similar to those of a clover, with three leaflets--in this case, the leaflets are somewhat rounded at the tips. Flowers appear in clusters at the ends of the branches. Each flower is pea-shaped, with five brilliant yellow petals. The petals are of three sorts. The uppermost petal is the largest, and is called the "standard". Two lateral petals are the "wings", and two lower petals, which closely envelop the stamens and single pistil, are called "keel" petals. This architecture is typical of many (not all) members of the bean family. We botanists are not unknown to fits of poetic description, and we refer to this flower form as butterfly-shaped, or "papilionaceous". (I will admit that this description requires a bit of imagination upon the part of the observer.) The ten stamens within the flower are all separate; note that in many members of the bean family, the stamens will occur in two groups or "brotherhoods": one group of nine, and another single stamen, all by itself. Following the flowers, snug little legumes or pods will form, each about an inch long, and sitting at the end of a little stalk. The pods eventually turn black.

[Answer: "Yellow wild indigo," Baptisia tinctoria]

John Nelson is the curator of the A. C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196, or email nelson@sc.edu.

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